The paper and board making processes contain warm process waters (e.g. 45-60° C.) that are rich in biodegradable nutrients and have a beneficial pH (e.g. pH 4-9) thus providing a good environment for the growth of microorganisms. The microbes in the process show biofilm-forming, i.e. surface-attached, growth and free-swimming, i.e. planktonic, growth. Several problems in the paper industry are caused by the biofilms, i.e. slime layers, which develop on the surfaces of the process equipments and can rip off from the surfaces. Biofouling of the machine surfaces and the loose biofilm/agglomerates can cause severe process disturbances: reduce water flow; block filters, wires, etc.; deteriorate the end-product quality, e.g. by causing holes or colored spots in the end product; or break the whole paper web. The biofilms are difficult to remove from the surfaces of the process equipment and often require the use of very strong chemicals.
For controlling the microbe growth e.g. biocides have been added to the process waters. Planktonic microbes have been efficiently controlled by the biocides; however, the use of biocides has not solved all biofilm problems in the paper or board machines. Several reasons exist for that, e.g. a wide variety of microbes are growing in the papermaking process and it is now also known that bacteria growing in a biofilm are generally more resistant to biocides than the planktonic microbes.
One of the present inventors, Kolari, M. has recently investigated the biofilm-formers in paper and board industry in Attachment Mechanisms and Properties of Bacterial Biofilms on Non-Living Surfaces, Dissertationes Biocentri Viikki Universitatis Helsingiensis 12/2003, Ph.D. thesis, University of Helsinki, Finland. In the study biofilm-formers were identified and their interactions investigated. Accordingly, the processes were found to comprise different types of biofilm-forming microorganisms: primary biofilm-formers that are capable of adhering to clean surfaces and secondary biofilm-formers which then adhere to the primary biofilms. The primary biofilm-formers seem to be a prerequisite for successful surface colonization of several other microbes in paper and board machines. E.g. Deinococcus geothermalis is a primary biofilm-former and strains of several Bacillus species adhere to the primary biofilms of this bacterium. Kolari, M. et al in Journal of Industrial Microbiology & Biotechnology (2003) 30, p. 225-238, describe more primary biofilm-forming bacteria. Amended with the newest, unpublished data, the relevant primary biofilm-forming microorganisms recognized thus far are: species Deinococcus geothermalis; genus Meiothermus, such as species M. silvanus or M. ruber, genus Azospirillum; genus Burkholderia, such as B. multivorans or B. cepacia; genus Porphyrobacter, such as P. cryptus; genus “Rubellimicrobium”; and genus Thermomonas, such as T. haemolytica or T. hydrothermalis. The primary biofilm-formers are typically moderately thermophilic, some with maximum growth temperatures as high as 67° C., and most of the strains showing the fastest growth at temperatures of 45 to 55° C. To overcome the problem with the biofilms in paper industry was, however, not discussed.
As stated above, in the context of slime formation in paper and board machines, it appears that the biofilm-formers are the most harmful microbes and their prevention would improve the functioning of the process machines and thus productivity of the process. For that purpose the present applicant has disclosed in the recent patent applications of FI 20021986 and FI 20021987 a new type of anti-biofilm agents, which are of a plant origin and can be used for the prevention of the formation of the biofilm and/or for removal of the already formed biofilm in a paper or board making process.
The efficient use of the biocides or said anti-biofilm agents would require an effective monitoring method. In paper industry, the typical monitoring method for the microbe growth is the cultivation of a sample of process water in laboratory. Such cultivation methods are, however, time-consuming and complicated, i.e. they take several days and require i.a. the use of various growth media for isolation and identification of different types of microbes in a sample. Moreover, it is known that the microbe growth in laboratory is culture-medium-dependent, thus part of the microbes present in a sample are often unable to grow under the laboratory conditions. Furthermore, the monitoring is typically focused on the free-swimming microbes. Efficient methods for monitoring the effects of anti-biofilm agents on the biofilm-forming microbes have been lacking. Therefore, e.g. biocides are conventionally used for non-selective inhibition of all microbes in the process, whereby high amounts of biocides are often required.
FI 95597 of the present applicant describes a device which can be used in laboratory or be brought in the paper process for producing a biofilm on the slides thereof. The biofilm is formed with pure yeast cultures or by placing the device into the process waters. The growth is analyzed by counting the number of yeast cells per cm2 using conventional plating methods. As already mentioned the plating method is time-consuming both for identifying the harmful microbes and for screening of e.g. a suitable biocide. Moreover, a part of the microbes in the biofilm may fail to grow on the culture medium.
U.S. Pat. Nos. 6,326,190 and 6,410,256 describe a method, wherein a bacterial biofilm is formed on a surface of a plurality of protrusions arranged in a device and the sensitivity of the biofilm to antibacterial agents are determined. However, in said methods the biofilm has been formed with the conventional time-consuming technique, i.e. by using pure cultures which are cultivated in laboratory, in a specific laboratory device.
Accordingly, there exists a need in the paper industry for more effective methods for monitoring the slime formation.